San Francisco General Hospital, the city's only top-level trauma center, treated 53 patients -- 27 adults and 26 kids -- from the accident, spokeswoman Rachael Kagan said. Five adults and one child remained in critical condition on Sunday.

Fifteen patients were treated and released from the UCSF Medical Center, spokeswoman Karin Rush-Monroe said.

Another 55 patients were treated at Stanford Hospitals & Clinics, while seven children went to the affiliated Lucile Packard Children's Hospital.

Seven patients were treated at St. Francis Memorial Hospital and five at St. Mary's Medical Center, spokeswoman Dee Mostofi said.

California Pacific Medical Center treated nine patients, including two children, with injuries such as compression fractures, rib injuries and leg injuries, spokesman Dean Fryer said. Four patients were admitted and are in stable condition.

Some of the most seriously wounded had head injuries, spinal cord damage causing paralysis or bleeding injuries inside the abdomen, said M. Margaret Knudson, chief of surgery at San Francisco General, at a press briefing Sunday.

"Some of our patients have been operated on twice already," Knudson said. "There are going to be many many more surgeries to come."

Two of those in critical condition arrived at the hospital with "road rash" on their back, limbs and face, suggesting they had been dragged over something, Knudson said.

Some patients weren't able to speak. Of those who could talk to doctors, most said they'd been seated at the back of the plane, Knudson said.

Doctors saw relatively few burns, Knudson said, even though the plane itself caught fire after the crash.

Knudon credited first responders and those doing triage on the scene for helping to save lives, because they prioritized the most severely injured patients to be sent to the trauma center first.

Spinal cord injuries can be some of the most serious injuries in a crash such as this, says Samir Mehta, chief of the orthopedic and trauma service at the Hospital of the University of Pennsylvania in Philadelphia. Mehta didn't treat any of the injured.

One survivor, Elliott Stone, told CNN that some passengers' heads hit the ceiling during the crash.

That sort of severe impact can compress the spine, much as someone might compress a Slinky, Mehta said. That can cause vertebrae -- the small bones that make up the spine -- to burst, throwing shreds of bones to the sides. Those shards can act like shrapnel to injure nerves.

Spongy discs located between vertebrae normally act like shock absorbers for the spine. But severe pressure can crush even those discs, Mehta says.

"If it gets compressed, the bone will literally burst," Mehta says. "It's like taking a egg and dropping a dictionary on it."

Doctors need to operate immediately to relieve pressure on the nerves to prevent paralysis, Mehta says.

Patients also can be paralyzed if their heads pitch forward during a crash, knocking their foreheads against the seat in front of them, says Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York.

That can damage the C1 vertebrae, at the base of the skull, said Glatter, who did not treat any of the crash victims.

Andre Campbell, a trauma surgeon who was on call at San Francisco General during the emergency, said he treated some severe abdominal injuries. In some cases, the mesentery, a tissue that connects the stomach and other organs to the back wall of the abdomen, was pulled away from the intestines, probably because of the force of the crash.

"Your body is built to sustain a certain amount of force," Campbell said. "The forces that you sustain in an air crash are larger than the body is able to take."